A breathing mask and other safety equipment can be equipped with or connected to a communication device in order to enable the user of the breathing mask to communicate with other persons. For example, a fire fighter wearing a breathing mask has to be able to communicate with other fire fighters of his team and with fire chiefs. Examples where a breathing mask is equipped with a radio communication device are described, for example, in publications GB2415316 and GB2421443. The communication device comprises an electro-acoustical transducer device that includes a microphone and possibly also a speaker element.
The internal acoustics of breathing masks is notoriously bad. In addition, the speech may often undergo further degradation from radio transmission, external voice amplifiers, telephony, and other aspect of the kind mentioned above and related to the transmission and/or the signal conversion between the electrical and acoustical forms. Furthermore, there may be a significant level of background noise for example in a working area of a user of a breathing mask. Therefore, there is a need to suppress such signal frequencies which represent the noise with respect to the signal frequencies which represent the speech so as to make the speech clearer in order to avoid potential communication problems. The clarity of speech is important because it might cause even a dangerous situation if speech of e.g. a fire fighter is misunderstood by his team and/or by fire chiefs. The suppression of the signal frequencies which represent the noise can be implemented with an electrical filter connected to the output of the microphone. The electrical filter, however, requires electrical power which is a critical factor especially in battery operated devices such as a communication device integrated with or connected to a breathing mask or other portable safety equipment.